As for both of prokaryotes and eukaryotes, DNA sequences transposable from one site to another site within a genome or between different genomes have been known, and generally called transposable elements. Most of such transposable elements encode, within their own sequences, a site-specific recombination enzyme (transposase) required for the translocation from one site to another site. Among such transposable elements, those having the smallest and simplest structure are called insertion sequence (IS).
Insertion sequences among microbial transposable sequences exhibit several characteristics. They have a size of about 1 to 2 kb, and have inverted repeat sequences of about 8-20 bp at the both ends. When an insertion sequence is inserted into a microbial chromosome, duplication of a target sequence occurs on the end side of the insertion sequence (Mobile Genetic Elements, Academic Press, New York, p.159-221 (1983)). Among microbial insertion sequences, well studied are those derived from Escherichia coli [Mol. Gen. Genet., Vol. 122, 267-277 (1973)], those derived from Shigella [J. Bacteriol., 172, 4090-4099 (1993)], those derived from acetic acid bacteria [Mol. Microbiol., 9, 211-218 (1993)], those derived from mycoplasma [Mol. Microbiol., 7, 577-584 (1993)] and the like.
On the other hand, as for methane-assimilating bacteria, there have been known inventions of a method for continuous production of oxidation products utilizing such bacterial cells (Japanese Patent Laid-open No. 5-3279, Japanese Patent Laid-open No. 54-3583), environmental cleanup through degradation of environmental pollutants utilizing methane-assimilating bacteria (Japanese Patent Laid-open No. 6-245761, Japanese Patent Laid-open No. 8-24905), fermentation method for converting methane into materials for protein production (Japanese Patent Laid-open No. 50-40788) and the like. Thus, they are industrially important microorganisms. However, any insertion sequence derived from methane-assimilating bacteria has not been reported so far.